The present invention relates to a truss construction for a passenger conveyor.
Passenger conveyors are e.g. escalators or moving walkways. Escalators are passenger conveyors that typically carry passengers between landings at different levels in buildings, for example. Moving walkways are usually used to carry passengers along levels extending horizontally or with only slight inclination.
An escalator or moving walkway typically includes a truss construction, balustrades with movable handrails, tread plates, a drive system and a step chain for engaging and propelling the tread plates. In an escalator the tread plates have the form of steps, while they have the form of pallets in case of a moving walkway. The step chain travels in an endless loop between turnaround sections located at an upstream landing and a downstream landing, respectively. The truss construction supports the other components of the conveyor and rests on a basement. The truss construction includes truss sections on lateral sides of the tread plates and extends in conveying direction. Each truss section has two end sections, the end sections on a respective longitudinal side forming landings, respectively. The end sections of a same lateral side are connected by an inclined or—in case of a moving walkway—possibly also horizontal midsection. One of the landings, e.g. in case of an escalator usually the upper landing, houses the drive system or machine of the passenger conveyor positioned between the trusses.
The drive system of an escalator or moving walkway typically comprises the step chain, a step chain drive sheave (e.g. in the form of a sprocket or toothed wheel), an axle and a drive motor. The step chain travels a continuous, closed loop, running from one landing to the other landing, and back. The tread plates are attached to the step chain through step chain axles. The step chain axles also support step chain rollers, which are guided by rails fixed to the truss construction, and thereby define the path of travel of the step chain and the tread plates. The drive motor drives the drive sheave which is, directly or via a further transmission, in a driving connection with the step chain.
In a common passenger conveyor the truss construction comprises a framework for supporting a plurality of rails which are arranged for guiding and supporting step rollers and step chain rollers which are mounted to the tread plates of the passenger conveyor and/or to the links of the step chain.
A section of such a conventional truss construction 1 is shown in FIG. 1. The conventional truss construction 1 comprises two pairs of longitudinal beams 21, 22. On each side of the conveyor one of the pairs extends in the longitudinal conveying direction of the conveyor. Each pair comprises a lower longitudinal beam 21 and an upper longitudinal beam 22 which is arranged above and parallel to the lower longitudinal beam 21. The lower longitudinal beam 21 and the upper longitudinal beam 22 of each pair are connected to each other by a plurality of generally vertical beams 14 and generally diagonal beams 24, forming a rigid framework on each lateral side of the conveyor in order to give the truss construction 1 the necessary rigidity and strength.
Cross plates 20 are mounted to at least some of the vertical beams 14. Crossbars 23 are fixed to the cross plates 20 connecting the two frameworks to each other.
A plurality of rails 18 for supporting step chain rollers and/or tread plates rollers are mounted to and supported by the cross plates 20. The guide rails 18 are fine machined from high strength steel, e.g. annealed steel or spring steel, to achieve satisfactory running characteristics of the rollers.
FIG. 1 shows only a section of the longitudinal beams 21, 22, the rails 18 and some of the diagonal beams 24, respectively, so that the longitudinal beams 21, 22, the rails 18 and some of the diagonal beams 24 appear to be cut off in FIG. 1. This, however, is caused only by the fact that FIG. 1 shows a section and not the entire length of the truss construction 1.
The individual beams 14, 21, 22, 24, cross plates 20 and rails 18 are made of steel and joined together by numerous welding connections to form a socalled truss. The cross plates 20 and rails 18 are fixed by adjustable holders and fixing parts to the truss.
The assembly and maintenance of such a conventional truss construction 1 is complex and expensive as it comprises a large number of different elements which have to be produced and mounted separately. The welding done in the factory requires knowledge and experience and involves complex apparatus to achieving the necessary exactness when mounting the guide rails, as the typical tolerances for the truss are some millimeters, while the typical tolerances for the guide rails are some tenths of a millimeter.
It is desirable to provide a truss construction for a conveying device which can be produced and mounted more easily with sufficient accuracy and with a minimum of adjustments needed.